'dma_request_chan_by_mask()' can not return NULL.
Try to keep the logic in 'no_dma:' by resetting 'qspi->rx_chan' in case
of error.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Mark Brown <broonie@kernel.org>
        dma_cap_set(DMA_MEMCPY, mask);
 
        qspi->rx_chan = dma_request_chan_by_mask(&mask);
-       if (!qspi->rx_chan) {
+       if (IS_ERR(qspi->rx_chan)) {
                dev_err(qspi->dev,
                        "No Rx DMA available, trying mmap mode\n");
+               qspi->rx_chan = NULL;
                ret = 0;
                goto no_dma;
        }